潮汐对长江口南支仔稚鱼种类组成及密度影响

Effect of tide on the species composition and density of the fish larvae and juveniles community in southern branch of Yangtze River estuary

为探讨潮汐对长江口南支仔稚鱼群落的影响,于2017年5月—2018年4月,在长江口南支的南北纵向断面设置两个站位点(St.1:31°35.500′N,121°20.004′E;St.2:31°33.500′N,121°20.000′E),于每月大潮期间采用大型仔稚鱼网(口径1.3 m,网目0.5 mm)按潮汐定时昼夜进行"表、中层"水平拖网采样(涨潮采样4次,退潮采样4次)。全年总计拖网384次,共采集到仔稚鱼51783尾,隶属于11科32种。优势种为贝氏■(Hemiculter bleekeri,占总尾数的87.05%)、鲫(Carassius auratus,占总尾数的3.45%)、翘嘴鲌(Culter alburnus,占总尾数的3.16%)、子陵吻虾虎鱼(Rhinogobius giurinus,占总尾数的2.16%)和香■(Repomucenus olidus,占总尾数的0.01%)。采集的仔稚鱼发育阶段主要集中在前弯曲期,占总数的95.21%,其次为弯曲期4.54%,后弯曲期0.12%,稚鱼期0.12%,卵黄囊期0.01%。研究结果表明,长江口南支水域各月平均密度及不同生态类型的渔获量均受不同程度的"涨退潮"影响,均表现为涨潮平均密度、渔获量大于退潮。长江口南支贝氏■、鲫、翘嘴鲌、子陵吻虾虎鱼、香■等5个优势种的体长及发育阶段分布因潮汐而变化,除子陵吻虾虎鱼外,其余4种仔稚鱼的体长分布均表现为夜间高于白天,5种仔稚鱼体长的周年分布呈显著月变化;除前弯曲期外,5个优势种均表现出退潮时弯曲期仔稚鱼的平均密度高于涨潮时,后弯曲期仔稚鱼的平均密度低于涨潮时。相关性分析结果表明,溶氧量、温度与平均密度之间存在显著相关性,盐度与平均密度之间无显著相关性。

To clarify the effect of tide on the fish larvae and juvenile community,fish larvae and juveniles were collected monthly at 2 stations(St.1:31°35.500′N,121°20.004′E;St.2:31°33.500′N,121°20.000′E)on the spring tide between May 2017 and April 2018.Sampling was conducted in North-South longitudinal section of the south branch of Yangtze River estuary,using a larval net(1.3 m mouth-diameter,0.5 mm mesh).Moreover,according to the tidal changes(4 flood tides,4 ebb tides),each haul was made parallel to the surface layer and middle layer.A total of 51783 fish larvae and juveniles were collected,representing 32 species from 11 families.The five dominant species was Hemiculter bleekeri(87.05%of the total),Carassius auratus(3.45%in total of the fish),Culteral burnus(3.16%in total of the fish),Rhinogobius giurinus(2.16%in total of the fish),Repomucenus olidus(0.01%in total of the fish).The pre-flexion stage was the dominant stage(95.21%in total of the fish),followed by flexion stage(4.54%in total of the fish),post-flexion stage(0.12%in total of the fish),juvenile stage(0.12%in total of the fish)and yolk-sac larval stage(0.01%in total of the fish).The results of average density analysis showed that the monthly average density and catches were affected by the flood tide and ebb tide to a certain extent:average density of flood tide is larger than that of the ebb tide.The five dominant species were affected by the changes of tide besides the Rhinogobius giurinus,the body length distribution of other four species both showed higher at nighttime than daytime,and the annual distribution of five dominant species showed obvious monthly changes.The developmental stage analysis showed that:except for the pre-flexion stage,the flexion stage of the five dominant species at flood tide were higher than those at the ebb tide,while the post-flexion stage in ebb tide were lower than those at flood tide.The results of ecological types analysis showed that the total fish collection of freshwater,brackish water and offshore at flood tide were greater than that those at ebb tide.The correlation analysis showed that there was a significant correlation between dissolved oxygen concentration,temperature and average density,but no significant correlation between salinity and average density.